improve tooltip accessibility with tab focus
improve tooltip accessibility with tab focus

allow tooltips to be rendered with keyboard tab focus
fixes CNVS-8935

Test Plan
1) Navigate to a page with tooltips
   (e.g. large roster group UI index page, see '+' add user icon)
   (e.g. localhost:3000/styleguide#tooltips)
2) Using keyboard navigation, tab over the tooltip item
3) Ensure tooltip is rendered correctly
4) Ensure tooltip is removed correctly when focus is tabbed away

Change-Id: Ifb84fe2862227fc26dbb297b9e0caa95e83e5cb0
Reviewed-on: https://gerrit.instructure.com/26133
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>
Product-Review: Marc LeGendre <d33c80bc45d65303e33ca83108a9952b745af9ef@instructure.com>
QA-Review: Marc LeGendre <d33c80bc45d65303e33ca83108a9952b745af9ef@instructure.com>

arrivu/hoodemo,whalejasmine/canvas-lms,redconfetti/canvas-lms,kyroskoh/canvas-lms,HotChalk/canvas-lms,jay3126/canvas-lms,greyhwndz/canvas-lms,gbleydon/canvas-lms,sdeleon28/canvas-lms,wrdsb/canvas-lms,juoni/canvas-lms,tgroshon/canvas-lms,redconfetti/canvas-lms,arrivu/qibla-ecampus,grahamb/canvas-lms,sdeleon28/canvas-lms,samuels410/greatlakes-lms,va7map/canvas-lms,narigone/canvas,matematikk-mooc/canvas-lms,roxolan/canvas-lms,redconfetti/canvas-lms,fronteerio/canvas-lms,efrj/canvas-lms,shidao-fm/canvas-lms,shidao-fm/canvas-lms,greyhwndz/canvas-lms,va7map/canvas-lms,samuels410/greatlakes-lms,AndranikMarkosyan/lms,usmschuck/canvas,landonwilkins/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,leftplusrightllc/canvas-lms,ShreniiNepal/shrenii_lmp,jay3126/canvas-lms,skmezanul/canvas-lms,dgynn/canvas-lms,ShreniiNepal/shrenii_lmp,HotChalk/canvas-lms,instructure/canvas-lms,skmezanul/canvas-lms,instructure/canvas-lms,dgynn/canvas-lms,Rvor/canvas-lms,Rvor/canvas-lms,antoniuslin/canvas-lms,va7map/canvas-lms,dgynn/canvas-lms,AndranikMarkosyan/lms,landonwilkins/canvas-lms,Unow/canvas-lms,Unow/canvas-lms,SwinburneOnline/canvas-lms,shidao-fm/canvas-lms,samuels410/greatlakes-lms,juoni/canvas-lms,AndranikMarkosyan/lms,fronteerio/canvas-lms,narigone/canvas,eCNAP/CANVAS,gbleydon/canvas-lms,dgynn/canvas-lms,leftplusrightllc/canvas-lms,antoniuslin/canvas-lms,Jyaasa/canvas-lms,efrj/canvas-lms,snehakachroo1/LSI_replica,arrivu/hoodemo,sfu/canvas-lms,wye0220/shindig-canvas,utkarshx/canvas-lms,va7map/canvas-lms,fronteerio/canvas-lms,roxolan/canvas-lms,matematikk-mooc/canvas-lms,roxolan/canvas-lms,usmschuck/canvas,djbender/canvas-lms,Rvor/canvas-lms,samuels410/greatlakes-lms,kyroskoh/canvas-lms,Jyaasa/canvas-lms,eCNAP/CANVAS,wimemx/Canvas,ShreniiNepal/shrenii_lmp,wrdsb/canvas-lms,greyhwndz/canvas-lms,whalejasmine/canvas-lms,redconfetti/canvas-lms,sdeleon28/canvas-lms,landonwilkins/canvas-lms,loganrun/pincan,narigone/canvas,greyhwndz/canvas-lms,leftplusrightllc/canvas-lms,grahamb/canvas-lms,jay3126/canvas-lms,gbleydon/canvas-lms,sfu/canvas-lms,arrivu/qibla-ecampus,eCNAP/CANVAS,matematikk-mooc/canvas-lms,shidao-fm/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,venturehive/canvas-lms,antoniuslin/canvas-lms,HotChalk/canvas-lms,instructure/canvas-lms,tgroshon/canvas-lms,landonwilkins/canvas-lms,AndranikMarkosyan/lms,instructure/canvas-lms,wrdsb/canvas-lms,loganrun/pincan,utkarshx/canvas-lms,Jyaasa/canvas-lms,utkarshx/canvas-lms,arrivu/arrivu-lms,SwinburneOnline/canvas-lms,arrivu/arrivu-lms,instructure/canvas-lms,kyroskoh/canvas-lms,SwinburneOnline/canvas-lms,usmschuck/canvas,sfu/canvas-lms,sfu/canvas-lms,snehakachroo1/LSI_replica,wimemx/Canvas,Jyaasa/canvas-lms,djbender/canvas-lms,skmezanul/canvas-lms,arrivu/qibla-ecampus,ShreniiNepal/shrenii_lmp,jay3126/canvas-lms,grahamb/canvas-lms,wye0220/shindig-canvas,efrj/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,arrivu/arrivu-lms,grahamb/canvas-lms,venturehive/canvas-lms,narigone/canvas,skmezanul/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,juoni/canvas-lms,venturehive/canvas-lms,roxolan/canvas-lms,tgroshon/canvas-lms,wrdsb/canvas-lms,instructure/canvas-lms,snehakachroo1/LSI_replica,wye0220/shindig-canvas,utkarshx/canvas-lms,wimemx/Canvas,eCNAP/CANVAS,antoniuslin/canvas-lms,tgroshon/canvas-lms,loganrun/pincan,efrj/canvas-lms,snehakachroo1/LSI_replica,whalejasmine/canvas-lms,juoni/canvas-lms,usmschuck/canvas,Rvor/canvas-lms,arrivu/hoodemo,whalejasmine/canvas-lms,leftplusrightllc/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,sdeleon28/canvas-lms,Unow/canvas-lms,kyroskoh/canvas-lms